I use lead wire from Corbins. Yes, it is considerably more expensive than raw lead, but the time and energy it takes to put that lead into core molds, really isn't worth it. Plus the lead fumes, possibility of getting burned, safety reasons, etc., makes it REALLY not worth it.
A 10 pound spool of Corbins lead wire, (I only swage .177, so I use their .170 wire) comes to 70, 000 grains of lead wire. If my average projectile weighs about 10 grains, I'll have about 60,000 grains of slugs, with that 10,000 grains being bleed off from the swaging process. That gives me about 6000 slugs for $50 worth of lead wire. Still reasonably economical in my book.
Tom Holland
Field Target Tech
Fieldtargettech.com